1. Field of the Invention
The present invention relates to a crosslinked elastomer body to be used as a material for a sensor of a resistance increasing type which is designed such that a resistance observed under compressive strain or bending strain increases according to the strain, and to a production method for the crosslinked elastomer body.
2. Description of the Related Art
Conventionally, inorganic strain sensors employing inorganic materials typified by piezoceramic materials are used for detecting stress, acceleration, vibrations and deformation (strain) exerted on a component. However, such an inorganic strain sensor is generally made of a highly rigid material, so that the shape design flexibility of the sensor is limited. Further, a specific sensor material system should be selected and prepared depending on a measurement range of surface pressure, strain, acceleration or the like. Therefore, the advent of a strain sensor capable of sensing a wider measurement range of a physical quantity with the use of the same material system is long-awaited.
In view of this, elastomers are employed instead of the inorganic materials, and a variety of pressure-sensitive electrically-conductive elastomeric materials are proposed which are each prepared by combining an elastomer with an electrically conductive filler (see, for example, Japanese Unexamined Patent Publication No. HEI3(1991)-93109).
The patent publication discloses a sensor of a so-called resistance reducing type which exhibits a higher electrical resistance under no strain but exhibits a reduced electrical resistance under compressive strain. More specifically, when the sensor is under compressive strain, inter-particle distances of the electrically conductive tiller in the elastomeric material are reduced, so that electrical conduction paths are formed by the electrically conductive filler to reduce the resistance. However, the sensor suffers from significant variations in detection value (resistance value) with respect to the strain, because a resistance change responsive to the strain is not necessarily constant. In some cases, the sensor exhibits an increased electrical resistance under greater strain. This makes it difficult to provide stable measurement results. The variations in detection value with respect to the strain occur not only between different sensors but also in a single sensor. The sensor tends to suffer from wider variations in detection value when being deformed in different directions. With less reliable measurement results, the sensor fails to provide sufficiently high measurement accuracy required for industrial applications.
A pressure-sensitive electrically-conductive elastomeric material for the resistance reducing type sensor disclosed in the patent publication significantly varies in detection sensitivity depending on the proportion of the electrically conductive filler blended in the elastomer. Therefore, it is difficult to impart the sensor with intended sensitivity and other measurement characteristics, making it very difficult to design and produce the sensor. Further, the sensor disclosed in the patent publication is simply adapted to detect a compressive deformation degree based on a change in DC resistance. After particles of the blended electrically conductive filler are brought into a certain contact state, the detection value hardly changes. Therefore, the sensor has a drawback such that the detection ranges of external force and stress are narrower.
As described above, the pressure-sensitive electrically-conductive elastomeric materials of the prior art have resistance reducing properties. However, a pressure-sensitive electrically-conductive elastomeric material having a pressure-sensitive resistance increasing property is hitherto unknown In addition, as described above, it is difficult to impart the prior-art elastomeric materials with intended pressure sensing characteristics and other measurement characteristics. Therefore, a sensor employing any of the prior-art elastomeric materials has a narrower measurement range.
In view of the foregoing, it is an object of the present invention to provide a crosslinked elastomer body which has a pressure-sensitive resistance increasing property, higher shape design flexibility and excellent moldability, and is capable of stably sensing a wider measurement range of a physical quantity when used for a sensor (a sensor of a resistance increasing type), and to provide a production method therefor.